In the case of a standard 5-MW wind turbine, the nacelle can carry a rotor made up of three blades (about 60 m long for example) that drives, through the agency of a gear reducer, the rotating part of an electric generator and accessories such as the blade orientation system, electric transformers, a hydraulic system, a ventilation system. The structure of the nacelle rests on a slewing ring itself supported by the tower.
The rotor plane is oriented into the wind. The nacelle is therefore rotatably mobile with respect to the axis of the tower, by means of one (or more) motor-driven gears cooperating with a ring gear. The overall weight of a nacelle can be of the order of 200 to 300 tons.
The approximately 100-m high tower supporting the nacelle rests on a floating support held in position by anchor lines in the case of water depths greater than 50 m.
Floating wind turbines comprise floating support and anchoring systems of various kinds, systems whose one purpose is to limit the movements and accelerations at the turbine under the action of the marine environment (wind, current, wave). However, the specific issue of floating wind turbines is that a significant overturning moment is created by the thrust force of the rotor in operation, applied approximately on the nacelle. When the wind turbine is stopped, the thrust force is reduced and its application point is offset downward.
Indeed, the rotor of the wind turbine undergoes many forces and stresses linked with the wind speed. This results in a thrust on the rotor supported by a thrust bearing. The value of this thrust force oriented in the direction of the wind depends on the angle of the blades (pitch) with respect to the direction of the wind.
One important parameter for dimensioning a floating wind turbine is the inclination of the floater (and therefore of the rotor) since wind turbines cannot operate above relatively moderate inclinations (typically some degrees).
It is therefore necessary to design a floater and its anchoring system so as to limit the list and the trim thereof, and a fortiori the pitch and roll motions.
Floating supports of all types (semi-submersible, spar, TLP), sized to limit pitch and roll motions notably under the effect of the overturning moment generated by the wind turbine, are known. These floaters are respectively based on the creation of a reaction moment under the action of hydrostatic stresses, weights or anchor tension. Thus, in wind power systems of the prior art, the floater provides the hydrostatic stiffness required to limit the inclination under the effect of loads.
However, relying on the dimensions of the floaters can generate, depending on the conditions of use, oversizing or even undersizing under exceptional conditions (strong winds, etc.).
The object of the present invention is to provide a particular layout for the anchor means so as to limit the list and trim, as well as pitch and roll motions, notably under the effect of the overturning moment generated by the wind turbine for a given floating support.